1. Field of the Invention
This invention relates to self-centering apparatus, and, in particular, to self-centering devices for introducing glass preforms into fiber drawing furnaces. Such devices are highly useful in the manufacture of low loss optical fiber. Accordingly, it is a general object of this invention to provide new and improved apparatus and devices of such character.
2. Description of the Prior Art
Various techniques for preparing low loss optical fibers involve initially preparing a preform using one of several vapor phase techniques. The preform, which is a rod of glass about 5 to 20 millimeters in diameter having the same relative radial variation in refractive index as desired in the fiber, is then fed at a controlled rate into a furnace where it softens and is drawn to a fiber by means of a drum or pinch wheel. Conventionally, fiber diameter is monitored and a protective coating is applied while the fiber is being drawn.
In prior art practice, the preform is held in a chuck while it is fed into the furnace. Horizontal alignment can be achieved by initially adjusting the preform position with respect to the furnace by means of micrometer screws; this horizontal position is then fixed through the vertical travel during a run.
The primary disadvantage of the foregoing technique arises from the fact that preforms are often not straight over their entire length because of the method of manufacture. Thus, a preform whose lower end is aligned with the furnace at the start of a run can go out of alignment during the run. This misalignment causes several problems in drawing optical fiber. First, misalignment results in radially non-uniform heating of the preform. This can cause the fiber to be non-circular and, in severe cases, can initiate contact between the preform and the element resulting in mechanical degradation of the resultant fiber and premature failure of the element.
The second problem caused by preform misalignment arises from the fact that turbulence in the furnace increases the magnitude of random fluctuations in fiber diameter. Conventionally, this turbulence, caused by air flow in the furnace, is controlled by irises at the ends of the furnace which are closed as much as possible around the preform on one side and fiber on the other. For preforms that go out of alignment during a run, the irises must be opened wide enough to pass the preform and fiber without contact throughout the run. This results in larger fiber diameter variations than is possible with irises that are more fully closed.
Another problem caused by preform misalignment is that the fiber being drawn becomes misaligned. This causes difficulties in fiber coating, where coating concentricity suffers, as well as in fiber diameter monitoring, where the fiber goes out of the measurement window.
3. Prior Art Statement
As a means of complying with the duty of disclosure set forth at 37 CFR 1.56, the following prior art statement serves as a representation that it includes, in the opinion of the applicants, the closest prior art of which they are aware. Though this statement should not be construed as a representation that a search has been made or that no better art exists, a concise explanation of the relevance of each listed item is that such art was enumerated in the course of a preliminary novelty search.
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,143,791 Lanahan et al. Aug. 11, 1964 3,396,598 Grispo Aug. 13, 1968 3,613,464 Archer Oct. 19, 1971 3,915,442 Marantette et al. Oct. 28, 1975 4,108,019 Martin Aug. 22, 1978 4,202,512 Nicholson, Jr. May 13, 1980 ______________________________________
Lanahan et al, U.S. Pat. No. 3,143,791, relates to a work positioning table for moving a workpiece relative to a template in any desired horizontal direction so that an associated machine can perform successive operations on the workpiece such as the insertion of components in a printed circuit board. The table includes a heavy base, a longitudinally-movable carriage, a transversely-movable platform for a workpiece, a flat front surface in the base for the template, and a stylus for mating with indentations in the template as the carriage and platform are moved on supporting rods and rails. The platform has a vertical opening which overlaps a carriage opening and a similar opening in the base so that vertical access to the workpiece is provided for extending a machine part therethrough for performing an operation on the workpiece. The movement of either the carriage or the platform or both is by means of ball bearings. When a locating means is centered, an operator uses both hands to depress switches to lower a plunger against resistance of a return spring for component insertion.
Grispo, U.S. Pat. No. 3,396,598, relates to a miropositioner which includes a linear slide mounted on a support; and a control lever which is mounted for universal movement about a pivot point substantially fixed relative to the base member of the linear slide. A first portion of the control lever is arranged to cooperate with the movable member in such a manner that movement of a second portion of the control lever more remote from the pivot point than is the first portion brings about related movement on a reduced scale of the movable member. The control lever is rotatable about its axis and is operatively connected with movable member and the support so that rotation of the control lever brings about movement of the base member of the linear slide relative to the support in a direction perpendicular to the plane.
Archer, U.S. Pat. No. 3,613,464, relates to apparatus for orienting beam directing or viewing apparatus having means for rotatably mounting a sensitive element of the device at the geometrical center of a spherical bearing. One end of a linkage arm is directly or indirectly connected to the device and the other end is then coupled to a mechanism which limits its motion to translation along either of two mutually orthogonal reference axes. Translation along either one of the two reference axes will cause the sensitive element to be rotated about the corresponding orthogonal axis without cross-coupling therebetween.
Marantette et al, U.S. Pat. No. 3,915,442, relates to a rectangular coordinate positioning system in which movement of an elongated carriage in a given direction at right angles to its long dimension is provided by a frame supporting parallel rails running in the given direction. The carriage is mounted to the rails for movement in this given direction. A torque tube has a longitudinal axis parallel to the longitudinal dimension of the carriage at right angles to the direction of the rails, the tube being mounted to the base frame for rotation about its own axis. Identically dimensioned coupling means are provided between opposite end portions of the torque tube and opposite longitudinal means constraining movement of the end portions of the carriage to precisely equal distances in the direction along the rails, respectively. A second pair of parallel rails can be mounted on the carriage to support a work table for movement in a direction at right angles to the first mentioned direction so that the work table itself can be positioned at any coordinate point.
Martin, U.S. Pat. No. 4,108,019, relates to a solar tracking device. A driving shaft, with its longitudinal axis extending parallel to the axis of rotation of the earth, is rotated at a constant speed. A frame is mounted for rotation in azimuth in a first plane which is angularly inclined with respect to the first axis. A tracking head is mounted on the frame for altitudinal rotation about an axis disposed in said first plane and which extends perpendicular to the azimuthal position of the sun with respect to the axis for rotation of the tracking head. Azimuthal drive means comprises a universal joint having a driving member connected to the driving shaft for rotation about its axis in an equitorial plane and a driven member connected to said frame for rotation in said first plane about the frame axis and a centre of gyration located at the intersection of said first axis and said first plane, the driven member being arranged such that its variable angular velocity is synchronized with respect to that of the sun about the frame axis to track the sun in azimuth, altitude drive means driving said tracking head about its axis to track the sun in altitude as said tracking head is driven about said centre of gyration.
Nicholson, U.S. Pat. No. 4,202,512, relates to a level layer winding method and apparatus in which wire can be wound in successive level layers on rotatively driven spools or reels.
Disadvantageously, none of the foregoing art suggests devices for self-centering. No teachings are suggested for use in the manufacture of low loss optical fiber. Some of the prior art fail to suggest rotational or swivel movement of a workpiece.
Another object of this invention is to provide for new and improved devices for holding a glass preform while it is being fed into a fiber-drawing furnace.
Still another object of this invention is to provide for new and improved apparatus for holding a workpiece, wherein the workpiece is self-centeredly supported.
Yet another object of this invention is to provide new and improved mechanisms for self-centering a glass preform during the manufacture of optical fiber without the necessity of operator intervention, and without undue monitoring and feedback schemes.
Still yet another object of this invention is to provide new and improved apparatus for providing high quality, low loss, optical fiber.
In accordance with one embodiment of the invention, a self-centering device for supporting a generally cylindrically shaped workpiece having a central axis includes a mounting frame having an opening therewithin. A pair of parallel, substantially horizontal shafts are mounted within the frame and traverse the opening. A first roller bearing is adapted for reciprocating movement axially along one of the shafts. A second rolling bearing is adapted for reciprocating movement axially along the other of the shafts. A first connecting rod is coupled to the first rolling bearing and to the second rolling bearing so that the resulting rod and rolling bearings combination can be reciprocated in a direction parallel to the axes of the shafts. Third and fourth rolling bearings are adapted for reciprocating movement axially along one and the other, respectively, of the shafts. A second connecting rod is coupled to the third rolling bearing and to the fourth rolling bearing so that the resulting rod and rolling bearings combination can be reciprocated in the direction parallel to the axes of the shafts. Separate connecting rod bearings are adapted for reciprocating movement axially along the first connecting rod and the second connecting rod, respectively. A spherical-seated, self-aligning bearing supports the workpiece so that the workpiece axis can be moved through an appreciable angle in any direction. A mounting carriage is coupled to the connecting rod bearings for housing the spherical-seated, self-aligning bearing for supporting the workpiece against a resultant of a force of tension along a generally downward direction and of a force due to gravity. In accordance with certain features of the invention, the appreciable angle in any direction includes a sweep of nor more than ninety degrees. The sweep can be, for example, twenty-eight degrees. The device can further include means for providing vertical movement to the frame. The two connecting rods can be parallel, and can be spaced apart a fixed distance regardless of orientation with respect to the frame. The four rolling bearings are all movable in unison in a direction parallel to the axes of the shafts, wherein each of the rolling bearings has an axis, and wherein a point on each of the rolling bearing axes form vertices of a rectangle. The workpiece can have a diameter not in excess of twenty millimeters. The workpiece can be adapted to rotate within the spherical-seated, self-aligning bearing.
In accordance with another embodiment of the invention, a self-centering device for introducing a generally cylindrically shaped, but possibly bowed, glass preform having a central axis into a fiber drawing furnace located below the device includes a mounting frame having an opening therewithin. A pair of parallel, substantially horizontal shafts are mounted within the frame and traverse the opening. First and second rolling bearings, respectively, are adapted for reciprocating movement axially along one and the other, respectively, of the shafts. A first connecting rod is coupled to the two rolling bearings so that the resulting rod and rolling bearings combination can be reciprocated in a direction parallel to the axes of the shafts. Third and fourth rolling bearings, respectively, are adapted for reciprocating movement axially along one and the other, respectively, of the shafts. A second connecting rod is coupled to the third and the fourth rolling bearings so that the resulting rod and rolling bearings combination can be reciprocated in a direction parallel to the axes of the shafts. Separate connecting rod bearings are adapted for reciprocating movement axially along the first connecting rod and the second connecting rod, respectively. A spherical-seated, self-aligning bearing supports the glass preform so that the central axis of the preform can be tilted at any angle of up to fourteen degrees from its normal vertical position. A mounting carriage is coupled to the connecting rod bearings for housing the spherical-seated, self-aligning bearing for supporting the preform against a resultant of a force of tension along a generally downward direction and of a force due to gravity, whereby all the rolling bearings are movable in unison in a direction parallel to the axes of the shafts. Each of the rolling bearings has an axis with a point on each of the rolling bearing axes forming vertices of a rectangle. The preform has a diameter not in excess of twenty millimeters. Vertical movement can be provided to the frame so that the preform can be lowered into the furnace. The preform is self-centering with respect to the device, without necessity of operation intervention, and without necessity of monitoring and feedback of electrical signals to the device. In accordance with certain features of the invention, the preform is adapted to rotate within the spherical-seated, self-aligning bearing.